Low specific weight metals such as pure titanium and titanium alloy materials consisting mainly of titanium exhibit high heat resistance, excel in such mechanical properties as toughness and wear resistance, and being highly biocompatible, do not harm living organisms in which they are embedded. They therefore have the potential for extensive utility not only in industry but also in dental prosthetics, plastic surgery and other such surgical and medical fields.
However, since titanium materials are very active and are therefore exceedingly difficult to work, it has only been possible to process them in vacuo using special equipment and techniques. Because of this, it has not been possible to fabricate dentures and other complex, intricate articles from titanium.
Prior art casting methods for low specific gravity metals include the centrifugal casting method and the single chamber remelting plate bottom turn-open method. Since low specific gravity metals such as titanium have low mass and experience rapid solidification by cooling, however, they cannot easily be cast down to ultra-fine feature portions by the centrifugal casting method because the initial casting pressure at the start of rotation in this method is too small.
In the single chamber remelting plate bottom turn-open method, on the other hand, since the metal on the remelting plate is melted by an arc discharge from above, low-temperature molten metal is cast first. In addition, since the molten metal is deprived of heat as is passes through the drip hole of the remelting plate, the temperature of the cast metal is low and it thus solidifies rapidly with cooling. This makes it difficult to cast down to the ultra-fine feature portions.
Moreover, since the melting and casting chambers are not shut off from each other in the single chamber structure, it is impossible to establish a gas pressure differential between two vertically disposed chambers. This also makes it difficult to cast down to the ultra-fine feature portions.
This invention provides a high differential pressure, ultra-fine feature casting method for low specific gravity metal exhibiting an excellent unoxidized surface.